Bad zSorting when zIndex is the same

[jorge-graca-sky]

Hi, I have been investigating why some Elements randomly pop in front of other in our app. This has revealed a bug in the lightning’s zSorting algorithm, it does not sort Elements with the same zIndex by updateTreeOrder.

The issue is on sortZIndexedChildren of ElementCore, on lines 2062 “// Merge-sort arrays;” it assumes both arrays are sorted, however same zIndex items may not be (since _updateTreeOrder change does not trigger _zIndexResort = true the a array may have unsorted items)

The logic that ensured this was removed on version 1.0.4: performance(updateTreeOrder): refactor, make simpler and (in most cas… · rdkcentral/Lightning@38285e0 · GitHub

My suggestion of fix:
#441

[frank-weindel]

Hi @jorge-graca-sky, do you have any reproduction code/steps that consistently cause the "random pop" issue? If it helps we have a playground now where you can easily build examples and share them with a link: https://lightningjs.io/playground/

[jorge-graca-sky]

Hi @frank-weindel, thanks for the quick reply! Here is the requested playground example:

1. To see the bug press left.
2. Can see the issue with _updateTreeOrder not begin sorted by pressing right (after pressing left).
3. Can fix the zSort algorithm by pressing down.

Playground example

[jorge-graca-sky]

Hi @frank-weindel, is the example understandable? Anything else I could help?

[chiefcll]

@uguraslan is this fixed - I think the bug needs to be closed

[frank-weindel]

@chiefcll I don't think this bug was ever addressed. Perhaps we should elevate it?

[uguraslan]

@jorge-graca-sky suggested PR #441 as a fix, we need to review the suggested fix.